ANALYTICAL EDITION
248
inclined to think this the most probable source of the greater part of the iron found in the washings. Whether or not the cutting tool plays an important part in adding iron to the sample depends upon the extent of contamination from other sources. The following results, obtained from analysis of a piece of blister copper, serve as an illustration: -IRON-
NATVRE OB SAMPLE Surface turnings, stellite Inside turnings, stellite Inside turnings, high-speed steel Washings from inside high-speed steel turninga Washinns from inside stellite turnings 5 Weighed as FezOa.
Unwashed
Washed
%
%
0.036” 0.00074 0.0018 0.00083 0.0019 0.00083 0.00104 0.00077
Vol. 4, No. 3
Here again the’washings from the steel-cut sample yielded more iron than those from the one cut with stellite. The amount, however, is so small in comparison with the difference between the percentages found in the washed and unwashed turnings as to be negligible. The above results indicate that it is advisable to wash samples of copper with dilute hydrochloric acid when an accurate determination of iron is desired.
_____
T,TTPWRATTTRM CTTli’n __-_-____
(1) Yoe, “Photometric Chemical Analysis,” Vol. I, p. 243, Wiley, 1928. RECEIVED November 10, 1930.
Specification of Color on Dyed Fabrics by Spectroanalysis E. M. SHELTON~ AND ROBERTL. EXERSON, Cheney Brothers, South Manchester, Conn.
T
B y a modification of i f s sample holder, the illumination was too narrow to facturer c o n t a i n many ~~~~~~l Electric recording analyter has give a representative view of a fabric sample, for barked shifts thousands of samples of been made applicable to analysis of color on in t h e r e c o r d e d ocdyed fabrics, either retained as curred w i t h c h a n g e s in t h e fabrics. A Program Of work for applying specstandards for color lines or in troanalysis to color on fabrics is described, position of the sample. This connection with dyeingformulas covering recording of color produced by individual was p a r t i c u l a r l y serious in a w h i c h they i l l u s t r a t e . As standards for commercial prodyestugs, standard color lines, commercial fabric with a distinct rib effect such as a bengaline, but it was duction, such samples are frematches, loss of color during fastness tests, f o u n d ,,hat e v e n in cornparaq u e n t l y open to suspicion of having become soiled or faded, and cdcdation of dYeformulas* tively smooth weaves the surface irregularities were sufficient and a p e r m a n e n t r e c o r d of the original condition of a sample would prevent occasional to cause noticeable shifts in the position of the curve cordisputes from this cause, Since commercial matches usually responding to changes in brightness with slight rotary shifts deviate in some degree from the standard, some numerical in the position of the sample in the sample holder. The measure of the discrepancies would be of great value in es- manufacturer changed the optical system so as to increase tablishing tolerances. Moreover, a numerical record defining the width of the area illuminated to approximately 3 mm., effecting some improvement. There still remained difficulty a color should be of value in systematic filing of the samples, A spectrophotometric analysis of the light reflected from in obtaining reproducible readings because of vertical shifts the colored sample is to the physicist the most satisfactory in the curve resulting from slight rotation of the sample when record and definition of the appearance of the sample. replaced in the holder. Figure 1 illustrates the curves obWhether the interpretation and use of such data by a textile tained from a sample of fabric when viewed in two positions manufacturer would be practicable has been open to question, 90 degrees apart. In the case of a satin this difference has but the time-consuming and expensive methods of color been observed to be as much as 55 per cent. analysis which until recently were the only ones available ROTARYSAMPLEHOLDER prohibited any extensive practical trials. The invention of automatic recording color analyzers, notably one by ProFollowing a preliminary demonstration of an experimental fessor Arthur C. Hardy a t Massachusetts Institute of Tech- rotary sample holder by the General Electric Company, an nology, subsequently developed and marketed by the General inexpensive sample holder of this type was constructed Electric Company, has radically simplified the task of prepar- and has proved highly satisfactory. Its construction is shown in Figure 2. A circular sample of fabric about 25 ing the spectrophotometric curves. The purpose of this paper is to describe the experience a t the mm. in diameter is cut out with a die and placed behind a laboratory of Cheney Brothers in recording the colors of glass window in t,he holder which is mounted on the end of the fabric samples in terms of spectrophotometric curves using shaft of a small motor. To correct for possible error due to the General Electric recording color analyzer with modifica- viewing the sample through glass, the magnesium carbonate standard is cut in the shape of a thin disk which may be tiom noted below. The recording color analyzer has been described elsewhere slipped into the sample holder behind the same glass window. by Hardy (a), and a general description will not be repeated. The motor is so mounted in the cabinet of the color analyzer The machine, as delivered to Cheney Brothers’ laboratory that the light strikes the sample at 90 degrees and is taken in January, 1930, was arranged to view an area of the sample off at 45 degrees exactly as in the original fixed sample holder, about 1 mm. wide and 18 mm. long. The sample was held the only difference being that the sample is rotated conin a fixed position. It was found at once that this band of tinuously. Experiments showed that the speed of rotation February 1.5, 1932, research chemist for the Tannin Corporation, may vary Over a wide range, and it is only necessary to avoid certain critical speeds a t which synchronism with the flicker LOO E. 42nd St., N. Y. C. HE files of a textilemanu-
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1.5, 1932
wheel occurs and a stroboscopic effect results. When this occurs, it is at once evident from the motion of the recording pen and can be stopped by a change in speed of the motor. A rheostat is installed in the motor circuit for this purpose. Motor speeds between 3000 and 10,000 r. p. m. were tried, and the lower speeds were found satisfactory.
1 6 8 (3
k k
b
WAVE
249
PREPARATION OF FABRIC SAMPLES It will be appreciated that satisfactory results depend not only upon the performance of the color analyzer but also upon the preparation of the sample. In trying to define a dyestuff, not in terms of a sample of the dyestuff as obtained from the manufacturer but in terms of its color value when applied to a sample of fabric, the dyeing technic is exceedingly important. In dyeing silk, perfect exhaustion does not usually occur in the laboratory and is seldom obtained in plant practice. Reproducibility of dyeings depends, therefore, upon exceedingly accurate standardization of the dyebath and the whole procedure for dyeing. In spite of marked improvement in dyeing technic acquired through the necessity for reproducibility and the evidence shown by the color analyzer of frequent deviations in dyeing uniformity, it is believed that at present the limiting factor in accuracy in these experiments is in application of the dyestuffs to the fabric rather than in the measurements obtained with the color analyzer. It is safe to say that one by-product of real value from the experience in this laboratory
.uwm IN u/u/n/cRoNc
FIGURE1. CURVESFOR A SAMPLE VIEWEDIN Two POsITIONs 90 DEGREES APART A. B. C
Warp vertical in stationary sample holder Warp horizontal in stationary sample holder Sample rotated
Referring again to Figure 1, there is shown the curve for a rotated sample as compared with curves obtained for the same sample viewed in two fixed positions 90 degrees apart. Figure 3 shows curves of samples of a satin and a crepe which were taken from goods accepted as a commercial color match. These illustrate the difficulty of comparing curves obtained with samples held in a fixed position and the good agreement of curves obtained from rotating samples. This confirms our assumption that the practical color matcher, when called upon to match fabrics of strikingly different construction, consciously or unconsciously matches the average appearance of one sample to that of the other with practically the result obtained by rotation in the color analyzer. CALIBRATION OF COLORANALYZER The color analyzer is calibrated and its correct adjustment is checked not only by running curves for magnesium carbonate, but by transmission curves for two glasses of known transmission values, one blue and one red. It has been the practice to make these tests once a day, keeping a permanent file of the curves obtained. All measurements made upon samples submitted are dated so that they may at any time be compared with the calibration curves for that day. Ex-
/
SrrEl DAW
/
&#/.w5 M"8,C
nr
,408
/,WAY
Maw,"c,%7u*
FIGURE2. ROTATING SAMPLE HOLDER
perience has shown that the calibration curves do not shift appreciably during any one day, so it has not been necessary to run them for each fabric sample tested. For convenience in subsequent calculations, the curve for magnesium carbonate is generally recorded on the sheet with those of samples analyzed.
WAM LENGTH /N MlLL/M/CRONS
FIGURE3. COMPARISON OF COLORS ON SATINAND CREPE SILKS A. Satin with warp vertical B Satin with warp horizontal C. Satin rotated
D. Crepe with warp vertical E. Crepe with warp horizontal F. Crepe rotated
with the color analyzer has been the growth of a consciousness of the possibility of more exact reproduction of dyeings and a resulting general improvement in laboratory practice. In the case of samples of fabrics obtained from mill production or from outside trade, there has been a limitation in the application of the color analyzer owing to the area of sample required for examination. Not only is a circular sample 25 mm. in diameter used in the present sample holder, but several thicknesses of the material have been necessary to avoid errors due to the light passing through the sample. In the case of thin goods such as voiles, as many as sixteen thicknesses have been found necessary, although in most fabrics three or four layers are sufficient. Printed designs seldom offer large enough areas of a given color to furnish the necessary samples. In piece dyed goodfi there is no trouble provided sufficient material has been submitted for test. At the time of this publication, although some measurements of color on yarn samples have been made, a completely satisfactory method of mounting the yarn sample has not been developed. The construction of the sample holder made it convenient to pack the space behind the glass with small bits of fiber clipped from the sample, but it was demonstrated that the curve obtained varied with the fineness of cutting of the yarn, and a more representative curve would be had if all the yarn fibers could be stretched smooth and flat behind the glass of the sample holder. With a larger sample holder
ANALYTICAL EDITION
250
.-W A E LEN%TH /N M/Ll/M/CROM
FIGURE4. FAMILY OF CURVESFOR BRILLIANT WOOLBLUE FFR APPLIEDON SILK CREPE
in which a square card could be mounted, this condition could readily be obtained using several layers of yarn wound around the card.
per cent. Of this series the 2.0 per cent dyeing was chosen as a standard of comparison for shipment testing. As a rule, a shipment of dyestuff which is within 5 per cent of the concentration guaranteed by the manufacturer is satisfactory provided the hue is correct. The increasing application of standardized dyeing in which a definite dyeing formula is supplied the dyehouse by the laboratory has made it necessary to keep strictly within these limits, a shipment of higher concentration being just as objectionable as one of lower concentration. Thus far, in shipment-testing, judgment has been passed first by the eye, and only those shipments which seem questionable have been tested further on the color analyzer to attempt to evaluate the exact percentage deviation or to prove a discrepancy in hue. As mentioned above, curves were obtained for a given dyestuff a t a series of different percentage dyeings, all being recorded upon one sheet of paper as illustrated in Figure 4. Since the light absorbed by the dyed sample is proportional (over a limited range of concentrations) to the logarithm of the Concentration of dyestuff taken up by the fabric, it is con-
APPLICATION IN PLANTCONTROL
Having obtained results with the color analyzer which indicated that under certain conditions significant curves could he obtained from fabric samples, the following outline was made as a program of work for establishing the use of the color analyzer in control testing in textile manufacture: I. Records of individual dyestuffs a. To assist in controlling quality of dyes purchased b. To furnish data for calculation of dye formulas 11. Records of regular color lines
a F
FIGURE 5. DATA FOR BRILLIANTWOOL BLUEFFR REPLOTTED FROM CURVES OF FIGURE4 AFTER CORRECTING FOR MAGNESIUM CARBONATE AS 100 PER CENT REFLECT~ON AND FOR COLORFROM UNDYED FABRIC 111. kecords of matches obtained in commercial production a. To accumulate data for tolerances in deviations from Rtafidard color lines IV. Records of wash tests and light tests on individual dyestuffs and standard color lines a. To accumulate data on which to establish tolerances for loss of color during these tests V. Calculation of formulas in terms of two or more dyestuffs required to produce a color on fabric from which a given spectrophotometric curve will be obtained
I. RECORDS OF INDIVIDUAL DYES For this purpose dyeings were made on a crepe fabric with each of the commonly used dyestuffs. Dyeings were made in each case with a series of percentages of dye (calculated, as is customary in dyeing practice, on the weight of the fabric sample), The values taken were 0.1, 0.5, 1.0, 2.0, and 4.0
Vol. 4, No. 3
0
July 15, 1932
I N D U S T R I A L A N D E N G I N E E R I N G CHELMISTRY
Li i
When the discrepancy is due to hue difference, i t cannot be expressed so conveniently. A typical case is shown in Figure 7. Here it is necessary to follow the procedure of multiplying successive ordinates along the curve by the values a t corresponding wave lengths for each of the three curves for the excitation factors, as established by the Optical Society of America ( S ) , and obtaining three new curves, the areas under which may be represented by simple numbers. This is a tedious procedure, requiring from one-half hour to one hour for a single curve, but will undoubtedly be simplified by the development of a mechanical integrator if industrial application brings about sufficient demand for such assistance. The integration has been facilitated by having a supply of
ili
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251
~
j
I
I
~
600
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W V € LENGTH /N M/LL /M/C'?ON8
FIGURE7. CURVESOF Two SAMPLESPOORLY MATCHED BECAUSE OF HUE P H Y S I O L O Q I C A L STIMULI C A L C D . FROM
A.
VIOLBT
228561 192284 Diff., yo 15.9
B.
0. 8. A. EXCITATION FACTORS GR~EN R ~ D 63599 47940 65160 54366 2.4 13.4
nificant but, as is pointed out later, the calculation involved is somewhat slow and tedious.
111. COMMERCIAL MATCHES For a time analyses were made of samples obtained from each dye lot in commercial production and compared with the standard sample each was intended to match. I n the case of 130 consecutive dye lots, only one lot had been criticized as off-shade by the regular inspectors, and curves obtained with the color analzyer indicated only one lot aside from this one to be very questionable. Since records of poor matches were more useful than those of satisfactory lots because the data were to be used for correlation between the discrepancies in the curves obtained by the color analyzer and the opinion of the regular inspectors on poor matches, it was necessary to dye up in the laboratory a series of approximately matched samples varying in exactness of match and have them classified by the inspectors. I t was also necessary to supply some simple numerical expression for the difference between two curves. When the two curves are practically parallel, as is the case in Figure 6, the difference is one of brightness only and may be expressed in terms of the difference in per cent of reflection a t some one wave length, or, if preferred, in terms of the difference in area beneath the two curves.
s= 8 t s n d u d EprCple M= sample t o be compared
FIGURE8. FORMUSED
FOR
CALCULATION
OF
FIGURE9. GRAPHICCORRELATION OF COLOR MATCHESWITH DIFFERENCES PRINCIPALLY OF BRIGHTNESS
forms printed in which the series of corrected ordinates may be entered. Figure 8 shows this form in which are entered the data from Figure 7 . It should be mentioned here that in any of these calculations the curve recorded by the analyzer must first be corrected, point by point, dividing by the ordinate of the magnesium carbonate curve at that wave length and multiplying by 100. When two curves for a match in question are each converted into excitation factors by the calculation outlined above, there are obtained three Dairs of values, anv or all of which may differ. If the two numgers in all three pairs agree closely, the samples must a p pear alike to t h e n o r m a l eye. In all poor matches the numbers in ope or more of these pairs differ markedly. Thus far the largest percentage difference found between corresponding excitation values has been taken as the expression of the difference between two such samples. To illustrate, if the difference in the blue is greater than that in either the green or red, the latter is disregarded and the difference between the samples expressed entirely in terms of the blue excitation values. This is only an approximation, but thus far it has proved satisfactory enough. Figures 9 and 10 show graphically the correlation in a considerable number of cases in which the judgment of regular inspectors has been compared with the measurements obtained with the color analyzer. They show rather a surprising , EXCITATION VALUES tolerance on the part of the trade. The allow-
-
i
252
Vol. 4, No. 3
ANALYTICAL EDITION
able discrepancy appears greater when the difference is one of brightness than when hue is involved. It must be appreciated that the severity or laxity of the inspector in judging matches is a direct indication of the tolerance allowed by the trade. The consistent use of the color analyzer to assist the inspector in passing doubtful lotp would do much to establish a more uniform standard for color matches.
Since the change in appearance of a properly dyed fabric after washing is chiefly one of brightness, it is comparatively simple to apply the color analyzer to obtain a numerical expression for the loss of color during this test. Typical curves from samples before and after wash test are shown in Figure 11. It is only necessary to express the change in terms of per cent difference in reflectance at any one wave Iength. It should of course be kept in mind that the color analyzer can give only a numerical value to the change that takes place during such a test, and the trade will establish the tolerances based upon commercial practice. However, a tolerance which can be expressed in numerical values is certain to become more uniform and less likely to lead to misunderstanding and disputes. LIGHTFASTNESS TESTS.Experiments on the fastness of the dyed samples to light were based on exposures to a carbon arc light in the Fade-Ometer. These curves are not so simply interpreted as those for wash tests, since in Some cases there is a change in brightness, but more commonly the action of the Iight causes a distinct change in hue. Typical curves are shown in Figure 12. The same calculation for comparing curves for commercial matches may be applied to curves before and after light exposure.
V. CALCULATION OF FORMULAS FROM CURVES FIGURE 10. GRAPHICCORRELATION OF COLORMATCHESWITH PREDOMINATING HUE DIFFERENCES
The use of the color analyzer has proved especially valuable in comparing goods of radically different construction in which individual persons frequently disagree as to whether or not a satisfactory match has 'been obtained. Attempts have been made to use measurements of dyed yarns to compare with measurements of the color in the fabric obtained from the yarns, but a completely satisfactory method of mounting the yarn sample has not been obtained.
IV. RECORDS OF SAMPLES AFTER FASTNESS TESTS WASHTESTS. Good washability of fabrics has come to be more and more expected by the customer] and in the case of silks very marked improvement in washability has been shown within the last 5 years. Standard methods of making wash tests have been fairly generally adopted, but the decision as to the degree of loss of color through the washing operation has been left to estimation by eye.
This section has been included in the outline for a program for application of the color analyzer to textile manufacture, but, because the preceding steps obviously needed to be developed first and because a t this time the ability to calculate the dye formula from the curvc is of less practical than theoretical interest, there are no data to report here. I n one instance, however, in which goods are dyed by a continuous method (the Cohoe process) ordinary experience in dye application was not adapted to establishing the continuous feed bath required. A study of the substantivity of individual dyestuffs using the color analyzer has proved a solution for this problem and is reported in R paper by W. P. and E. R. Cohoe (1). SPECIALAPPLICATIONS For development work in the laboratory where experiments may be carried out under controlled conditions, the color analyzer is invaluable. A simple illustrntion of a laboratory use has been the establishing of a test for the tarnishing action of velvets intended for the jewelry box trade. The color of a
MAY6 L€M?U /N #LL/M/CffUM WAVE
LENSTU
/N H/LL/#/CffON8
FIGURE11. CURVESOF SAMPLESBEFORE WASHTEFTS
FIGURE12. CURVESOF SAMPLESBEFORE LIGHTEXPOSURE
AND AFTER
-4. Victoria Blue B before washing B Victoria Blue B after washing, showing unsatisfaotory fastness C : Erie Scarlet 3B before washing D. Erie Scarlet 3B after washmg, showing satisfactory fastness
A
AND AFTER
Victoria Blue B before exposure
B: Victoria Blue B after 5 hours in Fade-Ometer, showing objectionable
change C. Erie Soarlet 3B before exposufe D. Erie Scarlet 3B after 25 hours in Fade-Ometer, showing good fastness
July 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
disk of silver is recorded in the analyzer before and after a standard exposure in contact with the velvet sample, and from the two curves obtained there may be calculated a numerical grading of the tendency of the velvet to tarnish the metal. CONCLUSION The work described in this paper is still in progress, but since this program of development may be applicable in other fields and of greater general interest than any detailed and final results, the authors have felt justified in publishing this work at this stage. The expense of the color analyzer and the necessity of an operator with somewhat specialized training will probably limit its use in a plant dyehouse where a simpler form of color comparator is better adapted if and when it is
253
necessary to supplement the trained eye of the dyer. Special laboratory applications and the use of the analyzer in mill control, particularly in establishing tolerances in commercial matches and for loss of color after wash and light tests, should justify a general recognition of spectrophotometric analysis in the textile industry in the near future.
LITERATURE CITED (1) Cohoe,
W. P., and E. R., IND.ENG.CHEM.,Anal. Ed., 4, 112
(1932). (2) Hardy, A. C., J. Optical SOC.Am., 18, 96-117 (1929). (3) Optical SOC.Am., Report of Committee on Colorimetry for 1920-21, Ibid., 6, 548 (1922). R E C E I V ~December D 28, 1931. Presented before the Division of Dye Chemistry at the 82nd Meeting of the American Chemical Society, Buffalo, N. Y., August 31 t o September 4, 1931.
Automatic Apparatus for Determination of Small Concentrations of Sulfur Dioxide in Air. I11 MOYERD. THOMAS, American Smelting €4 Refining Company, Salt Lake City, Utah
E
ARLIER papers of this The application of the acid-hydrogen peroxide tin tubing, which is unaffected method to the continuous analysis of traces of by t h e solutions e m p l o y e d . ibe the sulfur dioxide in air, as well as higher concen- The mercury valves described completely automatic a p p a r a t u s trations in smelter flue gases, is described, and for the determination of traces of ibeen n t hreplaced e first pby a p ethese r (2)poppet have s u l f u r d i o x i d e in air. This its application to fumigation studies for the valves. apparatus h a s now b e e n imabsorption of the gas by plants is compared with Slightly acidulated hydrogen analyses of the plants themselves for total sulfur, p e r o x i d e solution is used as proved and its application extended to the continuous analywith which indicate that these analytical a b s o r b e n t . I n the first and sis and recording of (1) small third of the uses for which the machines are capable of a high degree of preconcentrations of sulfur dioxide apparatus was d e s i g n e d , this cision in evaluating the concentration of sulfur solution contains a b o u t 0.003 in the f i e l d , w i t h a r a n g e of 0.01 to about 7.0 p. p. m.; (2) dioxide in air. per cent hydrogen peroxide and higher c o n c e n t r a t i o n s up to 0.0005 per cent sulfuric acid. about 6 per cent in flue gases which are low in sulfuric acid I n the second it contains more peroxide. The increased conbut contain appreciable amounts of carbon dioxide; and ductance of the solution, as indicated by a recording Wheat(3) the absorption of sulfur dioxide by plants in laboratory stone bridge, gives a measure of the amount of SO2absorbed. fumigation experiments in the range from less than 0.1 p. p. m. A typical assembly is shown in Figure 2, which is a photograph to 50 p. p. m. This paper describes the apparatus for the of a laboratory machine. The solution is fed from a large three purposes mentioned above, and submits confirmatory supply bottle, 1, into a constant-level bottle, 2, whence it analytical data on the absorption of the gas by plants. is measured in a 100-ml. pipet, 3, and placed in an absorber, The machines are built on an angle iron framework and 4. While the solution in one absorber is being aspirated, the are driven by a small motor operating through the appropriate solution in the other is replaced with fresh absorbent. The commercial reduction gears. Steady suction is obtained by photograph also shows the motor and reduction gears, 5, means of a small Crowell pump, and the air volume is meas- the gas meter, 6, the cams, 7 , and an assembly of 14 valves, 8. ured in a wet test meter, which may be provided with an FIELD MACHINE electrical contact on the 1-cubic foot dial, so that the air volume can be recorded on the chart with the sulfur dioxide The field apparatus is installed in a small well-insulated analysis. Steel cams, 5 inches (12.7 em.) in diameter, operate house, and the gas sample is drawn through a tin tube through the poppet valves as previously described (9). The valves the roof, the opening being provided with a screen to exclude are made from 0.635-cm. (0.25-inch) brass angle valves, as insects. The room is provided with a thermograph and in the illustrated in Figure 1, and are mounted in solder permanently winter is thermostated. The field apparatus aspirates each solution for 20 minutes, on a steel plate, care being taken to secure good alignment for the valve rods which are connected with the cam followers drawing about 15 liters of air per minute and recording each through universal joints. The valves have functioned per- cubic foot on the chart. This large volume of air causes an fectly over a period of more than 2 years. The heavy-wall appreciable evaporation of the absorbing liquid, with atflexible red rubber bellows will last more than 1year, and can tendant cooling, two factors which tend to compensate each readily be replaced. The apparatus is connected by block other. The absorbers are mounted snugly in heavy copper
